The present invention relates to a printer, particularly a matrix printer with impact producing print elements, arranged in a noise reducing case under the assumption that any movable part in the case is prone to produce noise. Moreover, it is assumed that the mechanically moving parts are mounted in some fashion to a frame.
Printers of the type to which the invention pertains, are used in some form as on-line printers in public or private places. They are used, for example, in conjunction with cash registers, in banks, near teller stations, in various forms of offices, in travel agencies, for example, for printing tickets, or the like. They are used for printing various kinds of documents, such as cash receipts, encoded documents or the like. It is also well known that many of these printers produce a high pitch rather annoying sound, not unlike a high speed saw or the like. If such a printer, for example, is used in an office, especially in conjunction with a word processor or the like, it is usually intolerable if the noise produced, particularly by more than one of these printers, exceeds a certain level, e.g. 55 dB. Stranger noise will definitely interfer with the concentration of other workers or even of the worker operating the printer.
Generally speaking, printers cause such noise for a variety of reasons. The basic reason is that the impacting print elements, the moving parts of the print mechanism generally, including, for example, a carriage on which the print elements are mounted, or the like, set up oscillations and vibrations in and of various parts with which they come in contact, the noise is, of course, produced inside the printer, and encasing the printer has, from an overall point of view, some noise attenuating effect, but practice has shown that a cover or the like is not sufficient, particularly if more than one printer is in the same room. Also, and depending upon the environment of the printer, it may well happen that it stands in some particular location which often for unforeseeable reasons is prone to undergo sympathetic resonance vibrations or the like. In fact, the particularly way of placing a printer may tend to actually increase the noise it produces even in those cases in which there is a cover.
It is immediately obvious that the impact producing elements (hammer styli, etc.) produce noise just by virtue of the respective impact. However, there are other though related noise sources. One has to cope here with a variety of characteristic resonance frequencies of and in the printer, particularly of various parts thereof, of the frame, of the mechanisms as a whole, or of groups of elements which are interconnected in a compact fashion. Interconnected parts form an element which is mounted in some fashion inside the printer. The parts themselves and the interconnected unit each may undergo their own vibrations. These vibrations, whatever their original sources, may emerge into the ambient air from inside the housing; they may propagate as noise immediately and directly from the point of production. However, if the source is a point, it has to be observed that the vibrations are propagating through solid parts and emerge in different locations including the outside, as far as the casing is concerned. In the case of sympathetic vibrations relatively large parts vibrate as a whole and anything they hit sets up additional noise etc.
Generally speaking, a printer is constructed such that there is a frame to which all or most parts are connected. The frame is mounted in a printer housing. These two parts, namely the housing and the frame, are bolted together and the entire unit may be placed on some support surface. For example, rubber, or any other sound attenuating feet may be provided on the other side of the housing by means of which the printer is then placed onto whatever support surface is available.
This is the general background, and has to be taken into consideration if one attempts to provide for any noise abatement and noise attenuation.